This invention relates to the manufacture of metal matrix composites having high particulate loadings and, more particularly, to the concentration of composite materials with lower particulate loadings to achieve higher particulate loadings.
Metal matrix composites, for example those consisting of refractory particles such as silicon carbide or alumina distributed in aluminum alloy matrices, are most economically manufactured on a large scale by mixing techniques. One such technique, described in U.S. Pat. No. 4,759,995, disperses and wets refractory particles with molten metal using a shearing technique while avoiding the retention and incorporation of gases. Such mixing techniques are frequently restricted to relatively low particulate loadings (e.g. less than about 25 volume percent particulate) because of fluidity problems encountered during mixing.
On the other hand, metal matrix composites used in large-scale shape casting processes and similar applications most frequently use the same or lower solids loading because of similar fluidity constraints. As a result, scrap material from such casting processes having relatively low particulate loading is frequently available as a byproduct from such operations.
Higher solids-loading material is typically prepared by pressure-assisted or other infiltration techniques. These higher solids-loading materials are useful in certain structural and electronic applications, but because of the difficulty in producing and processing such materials, they have not found wide application.
There is a need for a less costly method for manufacturing higher solids loading metal matrix composites, ideally one which uses the proven cost advantages of the various processes for manufacturing low solids loading materials or which uses available scrap materials. There is further a need for methods for manufacturing high solids loading materials that can be readily cast, forged or otherwise manufactured by methods suitable for high volume production. The present invention fulfills this need, and further provides related advantages.